Low profile two-antenna assembly having a ring antenna and a concentrically-located monopole antenna

ABSTRACT

A disk-shaped two-antenna assembly contains a CP ring-antenna and a linear-monopole-antenna. The bottom surface of a ring-shaped dielectric member holds a ground plane. A circular radiating element is located on a top surface of the ring-shaped dielectric member. A linear radiating element is positioned coincident with a central axis of the two-antenna assembly, and a top end thereof carries a metal disk that extends perpendicular to the central axis of the two-antenna assembly. A centrally-located void lies between the ground plane and the metal disk to provide for the housing of electronic components. Metal RF shields are electrically connected to the ground plane and are located at the top portion of this void, intermediate the bottom-located ground plane and the top-located metal disk.

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional patent application claims the benefit of U.S.Provisional Patent Application Ser. No. 60/380,444, entitled “LOWPROFILE TWO-ANTENNA ASSEMBLY HAVING A RING ANTENNA AND ACONCENTRICALLY-LOCATED MONOPOLE ANTENNA” filed by Court E. Rossman onMay 13, 2002, incorporated herein by reference.

BACKGROUND OF INVENTION

1. Field of the Invention

This invention relates to the field of wireless communication, and morespecifically to antennas for radiating and receiving both circularpolarized (CP) and linear polarized electromagnetic signals, for examplesignals that are used in satellite communication systems.

2. Description of the Related Art

Mobile satellite communication systems create a need for low profile andcompact antennas. For example, satellite radio systems include bothsatellite transmitters and terrestrial or land-based transmitters, andmobile antennas that are used in these satellite radio systems arerequired to receive both satellite transmitted signals and terrestrialtransmitted signals. In addition, this signal redundancy must bedesigned into the system so that there will be few geographic regionsproviding gaps in coverage across the country.

Terrestrial signals are much stronger than satellite signals. However,in order to be economical, terrestrial transmitters are usually placedaround large metropolitan centers, since it is cost prohibitive to placeterrestrial transmitters in relatively unpopulated regions of thecountry. However, satellite signals are provided virtually everywhere,and such signals are required for regions of the country that do notreceive terrestrial transmitted signals.

A low profile satellite antenna is desired for automotive applicationsdue to obstacles that such an antenna may encounter, for example soccerballs, rollers that are within a car wash, and items that may betemporarily mounted on the roof of the automobile.

A low profile automobile antenna is also desired because such an antennacan be easily factory-installed, and the antenna runs less risk of beingdamaged before arriving at an auto dealership. An additional reasonfavoring low profile automobile antennas is their relatively pleasingappearance, and the fact that low profile antennas do not generallysuppress visibility.

In the example of a satellite radio system, it is a technical challengeto fit desired antenna functions within a single, low profile andcompact antenna assembly for mounting on the top of an automobile.

A low profile CP patch antenna is usually not adequate to serve as asatellite antenna, unless the automobile is located relatively close tothe equator. The directivity of a patch antenna that is located over alarge ground plane is usually over 5 dB when the antenna points directlyup.

From the vantage point of geographic areas within the United States,geo-stationary satellites are located predominantly between 20 and 60degrees off of the southern horizon. Hence, signals that are receivedfrom a geo-stationary satellite using a CP patch antenna are weaksignals.

A solution to providing a satellite antenna is a quadrifilar helixantenna. FIG. 1 shows a standard-technology antenna 10 having both aquadrifilar helix 11 and a concentrically-located monopole 12.Quadrifilar helix antenna 11, when fed in quadrature, generates an omniCP depressed cardioid pattern, which is an omni pattern with a moderate(i.e. a few dB) dip in gain at zenith. Monopole antenna 12 generates alinear omni pattern. Coupling between CP quadrifilar helix antenna 11and monopole antenna 12 can be reduced by placing the monopole antenna12 in the geometric center of helix antenna 11.

Quadrifilar helixes 11 as shown in FIG. 1 are typically over twowavelengths tall, this height being required in order to generate adepressed cardioid pattern. As can be seen from FIG. 1, such an antennadoes not have a low profile, and such an antenna is not physicallycompact.

A lower profile standard-technology antenna is a crossed dipole antenna,wherein the dipole must be ⅜ wavelength or more above a ground plane inorder to generate a depressed cardioid pattern. If the dipoles of suchan antenna are closer to the ground plane, directivity of the antenna istoo large, and the antenna pattern is similar to that of the CP patchantenna described above.

FIG. 2 shows a standard-technology droopy crossed dipole antenna 13having four combined monopoles 14 that are fed 90 degrees out of phasein order to generate CP radiation. The four meanderline monopoles 14 ofFIG. 2 are fed in phase and they are combined underneath the antennawith a feed network (not shown), to thus provide a single linearmonopole pattern. Monopoles 14 of FIG. 2 can be straight wires, they canbe planar inverted-F antennas (PIFAs), or they can be top loadedmonopoles, all of which create the same radiation.

Coupling between the crossed dipoles 15 of FIG. 2, and feed to monopoles14, is ideally zero because coupling to each of the four monopoles 14 isin quadrature, and this coupling cancels at the input to the antenna'sfeed network. However, the ⅜ wavelength height that is required inantenna 13 does not provide a low profile antenna for mounting on thetop of an automobile.

Low profile antennas that generate a conical CP pattern and that have adeep null at zenith, instead of a depressed cardioid pattern, areavailable. FIG. 3 shows a standard-technology ring antenna 16 thatoperates in TM₂₁ mode, antenna 16 having a field coupling feed 17 and asingle mode separator 18 that is located at 22.5 degrees from feed 17(see H. Hakano, K. Fujimori, J. Yamauchi, “A LOW-PROFILE CONICAL BEAMLOOP ANTENNA WITH AN ELECTROMAGNETICALLY COUPLED FEED SYSTEM,” IEEETrans. On Ant. And Prog., Vol 48, No. 12, December 2000).

One problem in providing a low profile antenna is that of antennabandwidth. Bandwidth typically is proportional to the distance betweenthe antenna radiating/receiving element(s) and the antenna ground plane;i.e., the volume of the antenna (see Chu, L. j., “PHYSICAL LIMITATIONSOF OMNI-DIRECTIONAL ANTENNAS”, J. Appl. Phys, Vol 19, December 1948, pp.1163-1175). Hence, it is advantageous to provide that theradiating/receiving element (herein after radiating element) of a lowprofile antenna be at the greatest distance above the ground plane as ispossible, while still satisfying the low profile requirement.

SUMMARY OF INVENTION

This invention provides a thin, disk-shaped, two antenna assembly foruse in radiating and receiving both CP and linear electromagneticsignals of the type usually used in satellite communication systems.

In accordance with the invention, a CP ring antenna and a top-loadedmonopole antenna occupy a common disk-shaped, or cylindrical-shaped,volume that has a generally flat bottom surface generally parallel to aflat top surface.

A ring-shaped radiating element of the ring antenna and the top loadingdisk of the monopole radiating element occupy a common plane at, oradjacent to, the generally top flat surface of this disk-shaped volume.That is, the radiating element of the ring antenna and the radiatingdisk of the monopole antenna may be generally coplanar.

The generally flat bottom surface of this disk-shaped volume includes ametal ground plane that may be carried by the bottom surface of agenerally flat printed circuit board (PCB). In use, it is intended thatantenna assemblies in accordance with the invention be physicallyoriented such that the ground plane is located in a generally horizontalplane.

The top-loaded monopole antenna (which may comprise two parallel andvertically extending metal posts) is located approximately concentricwithin the ring antenna in order to minimize electromagnetic couplingbetween the monopole antenna and the ring antenna. The top-loadedmonopole antenna is physically supported by the PCB, and an airdielectric is associated with the monopole antenna.

Electronic components that are used by the monopole antenna and/or thering antenna are located within a ring-shaped void that exists between adielectric ring whose top surface supports the ring antenna. Theseelectronic components may be mounted on the top surface of the groundplane at a location that is under the radiating ring of the ring antennaand under the top-loading disk of the monopole antenna.

The metal ring of the ring antenna may be in the form of meanderingmetal line that forms a circle, or it may be in the form of a wide or anarrow metal line that forms a circle. Metal perturbations or modeseparators cooperate with this metal ring in order to preserve thesymmetry of the ring antenna and in order to retain a symmetricalradiation pattern for the ring antenna.

At least one metal feed post is provided for the metal ring of the ringantenna and at least one generally centrally located metal post formsthe monopole radiating element.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a standard-technology antenna having both a quadrifilarhelix and a concentrically-located monopole.

FIG. 2 shows a standard-technology droopy crossed dipole antenna havingfour combined monopoles that are fed 90 degrees out of phase in order togenerate CP radiation.

FIG. 3 shows a standard-technology ring antenna that operates in TM₂₁mode, the antenna having a field coupling feed and a single modeseparator that is located at 22.5 degrees from the feed.

FIG. 4 shows a disk-shaped, two antenna assembly in accordance with theinvention that includes a ring antenna and a linear monopole antennathat is located concentrically within the ring antenna, wherein the ringantenna's radiating element comprises a wide-trace, non-meanderline,circle or ring-shaped metal pattern, and wherein the top portion of theantenna assembly includes two centrally-located and half-octagonal metalshields that are electrically connected to the assembly's ground planeand that operate to shield electronic components that are containedwithin an open volume of the antenna assembly at a location that isunder the two metal shields.

FIG. 5 shows a disk-shaped, two-antenna assembly in accordance with theinvention that includes a CP ring antenna of a given height and a linearmonopole antenna that is located concentrically within ring antenna andis of generally the same given height, wherein the ring antenna'sradiating element comprises a narrow-trace meanderline metal pattern.

FIGS. 6A and 6B respectively show the S-parameters versus frequency andthe Smith chart of the FIG. 5 two-antenna assembly.

FIGS. 7A and 7B show an embodiment of the invention that is similar toFIG. 5 wherein a two-antenna assembly includes two metal feeds for thering antenna in order to generate CP excitation.

FIGS. 8A and 8B show other techniques in accordance with the inventionfor applying metal perturbations to the CP ring antenna in order togenerate self-resonance in the absence of an externally-locatedquadrature feed network.

FIG. 9 shows an embodiment of the invention wherein a two-antennaassembly includes a monopole antenna and a ring antenna having arelatively narrow-trace metal ring in the form of a circle for producingthe TM₂₁ mode of operation.

FIG. 10 shows an embodiment of the invention wherein a two-antennaassembly includes a centrally-located monopole antenna and a relativelywide TM₂₁ solid-patch ring antenna, wherein the top metal disk of themonopole antenna can be placed coplanar with the radiating element ofthe ring antenna, or wherein the top metal disk of the monopole antennacan be located above the plane of the radiating element of the ringantenna as shown, and wherein cutouts are provided in the assembly'sdielectric member to selectively provide inductive loading of the ringantenna.

FIG. 11 shows an embodiment of the invention wherein the antenna of FIG.4 is placed on a metal pedestal that acts as ground plane for theantenna, this metal pedestal being used when the antenna is placed, forexample, on the metal roof of an automobile.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Without limitation thereto, embodiments of antennas in accordance withthis invention operate at 2.33 GHz, i.e. the frequency of interest forcurrent satellite radio communications. This constraint provides a wayto compare dimensions of different antennas, wherein the dimensions canalso be compared to wavelength. However, antennas in accordance with theinvention can be scaled to size to radiate at any frequency.

FIG. 4 shows a thin and disk-shaped two antenna assembly 100 inaccordance with the invention that includes a ring antenna 101 and alinear monopole antenna 102 that is located concentrically within ringantenna 101. Monopole antenna 102 can be characterized as a terrestrialtop-loaded metal disk monopole antenna that is shunt matched.

The ring antenna's radiating element 103 comprises a wide-trace,non-meanderline, ring-shaped metal pattern. The top portion of antennaassembly 100 includes two centrally-located and half-octagonal metalshields 104 and 105 that operate to shield electronic components (notshown) that are contained within a volume of antenna assembly 100 thatis under metal shields 104, 105.

Monopole antenna 102 is made up of two generally parallel metalradiating elements 120 and 121 whose top ends support a metal disk 122.

Antenna assembly 100 occupies a thin disk-shaped or cylindrical volumehaving a central axis 110, a height (see dimension 23 of FIG. 50 and anouter diameter (OD) (see dimension 37 of FIG. 5) wherein the heightdimension is much smaller than the OD. By way of a non-limiting examplethe height dimension of antenna assembly 100 is about 8 millimeters(mm), whereas its OD is about 75 mm.

The cylindrical volume that is occupied by antenna assembly 100 has agenerally planar bottom surface that includes metal ground plane 111 anda generally planar top surface that is generally parallel to groundplane 111. This cylindrical volume can be divided into threesub-volumes.

The first sub-volume of antenna assembly 100 is a ring-shaped volumehaving an inner diameter (ID) and an OD, whose lower surface comprises aring-shaped portion of metal ground plane 111, whose middle portioncomprises a ring-shaped dielectric ring 112, and whose upper surfacecontains the ring-shaped metal radiating element 103 of ring antenna101.

It will be noted that in the FIG. 4 embodiment of the invention thediameter of ground plane 111 is somewhat greater than the diameter ofring-shaped dielectric ring 112. The diameter of ground plane 111 can bemade generally 20 percent greater than the diameter of ring-shapeddielectric ring 112, as it is in other embodiments of the invention thatwill be described.

In an embodiment of the invention ground plane 111 extended beyond theOD of ring-shaped dielectric ring 112 an amount that is at least equalto the height of dielectric ring 112, in order to contain the antenna'sfringe E fields, and in order to allow antenna 100 to not vary in tuningon and off of a larger ground plane. An optimal size for ground plane111 is discussed below.

Dielectric ring 112 may be formed of a continuous ring of dielectricmaterial, or it can be formed of four 90-degree segments as is shown inFIG. 4. The plastic an dielectric material of dielectric ring 112provides structural support and dielectric loading, resulting in a sizereduction of antenna 100. The dielectric constant (DK) of thisdielectric material should be relatively low in order to retain antennabandwidth, however the DK should be large enough to fulfill the desiredrequirements for antenna size. Sample materials with a low DK and lowlosses are the brand GE NORYL of polyphenylene ether and the brandQUESTRA of syndiotactic polystyrene, a glass-filled crystalline polymerbased on a styrene monomer.

Ground plane 111 lies in a plane that is generally parallel toring-shaped radiating element 103, and ground plane 111 may be providedby a PCB whose lower surface is metallized to provide ground plane 111.

The second sub-volume of antenna assembly 100 is a cylindrical void thatis defined by the ID of dielectric ring 112. This second sub-volumeprovides space in which to mount electronic components (not shown) thatare associated with antenna assembly 100. In accordance with a featureof the invention, the top surface of this second sub-volume includes theabove-mentioned two centrally-located and half-octagonal metal shields104 and 105 that are electrically connected to ground plane 111 and thatoperate to RF-shield electronic components that are contained withinthis second sub-volume at a location that is under metal shields 104,105. In an embodiment of the invention the two metal shields 104, 105where generally coplanar and occupied a plane that was under the planeof metal disk 122, generally parallel to disk 122 and ground plane 111.

The third sub-volume of antenna assembly 100 is a mid-located andcylindrical shaped volume that includes a portion of the above-describedsecond sub-volume. The bottom surface of this third-sub-volume containsmetal ground plane 111, its center includes the two metal monopoleradiating elements 120 and 121 that extend generally perpendicular toground plane 111 and are electrically isolated from ground plane 111,and its upper surface contains the metal loading disk 122 that iselectrically connected to the top end of the two metal monopole elements120 and 121.

While two monopole elements 120, 121 are shown in FIG. 4, other monopoleconfigurations, including the use of one monopole element, are withinthe spirit and scope of the invention.

Rectangular cutouts 130 are provided on the outer circumference of thering antenna's radiating element 103, these cutouts operating as modeseparators that lower the capacitance of one of the antenna TM₂₁ modesand raises that mode's resonant frequency. By breaking the degeneracy ofthe two TM₂₁ antenna modes, CP radiation is generated.

Note that the two RF-shields 104, 105 are placed inside of ring-shapedradiating element 103, at a location whereat the E-fields fromring-shaped radiating element 103 are not strong. Thus, ground plane 111is effectively raised to the plane that is occupied by RF-shields 104,105 in this E-field-empty region of antenna assembly 100 withoutimpacting bandwidth or efficiency.

With reference to an optimal physical size or area for ground plane 111,antenna 100 with its built-in metal base or ground plane 111 performswell in free space, and when antenna 100 is associated with a muchlarger area ground plane.

Although a TM₂₁ antenna generally requires a ground plane of some sort,a very small-area ground plane is generally better than an infinite-areaground plane. For satellite reception, a small-area ground plane stopsbacklobe radiation sufficiently, and provides better radiation at 20degrees, when compared to an infinite-area ground plane. Aninfinite-area ground plane generally prohibits CP radiation along thehorizon. However, a ground plane should be either small (generally lessthan about 115 mm diameter) or large (generally greater than about 305mm diameter) so as to not adversely affect terrestrial gain.

In an embodiment of the invention TM21 antenna 100 of FIG. 4 had an ODof about 76 mm. When this antenna was mounted on a non-conductivesurface, a ground plane 111 having an OD of about 115 mm was used. Useof this size ground plane 111 provided minimal backlobes and good20-degree radiation for a satellite pattern. This 115 mm diameter groundplane also provided adequate terrestrial gain at the horizon, whichusually requires either a much smaller ground plane or a much largerground plane. A moderately larger ground plane (for example about 153 mmdiameter) reduces the terrestrial gain by an additional 2 dB. However,when the diameter of the ground plane is very large, this terrestrialgain recovers.

That is, antenna in accordance with this invention are associated witheither a large-area metal ground plane, for example the 1 meter or soarea of the metal roof of an automobile, or the antenna include abuilt-in metal ground plane or metal base that is about 100 mm indiameter, an example utility of such a built-in-metal-base/ground-planeantenna being for mounting on the plastic dashboard of an automobile.

The dimensional area of such a built-in metal ground plane or base ischosen such that the antenna's radiation patterns are good, and suchthat a large-area ground plane is not required. The use of only amoderately larger area or diameter ground plane may negatively affectthe antenna radiation patterns when the antenna is mounted on a plasticmember. Thus the diameter of a built-in ground plane should be chosenwith care, for example from about 100 to about 115 mm. Of course, theantenna's radiation patterns are also acceptable when such an antenna isused with a very large-area or large-diameter ground plane, since it isonly what might be called intermediate-area ground planes that canprovide a problem.

The built-in metal ground plane 111 shown in FIG. 4 provides aneffective ground plane for antenna 100 when antenna 100 is mounted on aplastic member such as the dashboard of an automobile, and when antenna100 is mounted on the large metal surface that is provided by the top ofan automobile, this metal automobile surface provides an effectiveground plane for the antenna.

As will be described relative to FIG. 11, when an antenna in accordancewith this invention is to be mounted on a unknown surface, for example ametal surface of the above-mentioned intermediate-size, a can-shapedmetal pedestal 400 is provided as the base of the antenna. Metalpedestal 400 elevates the antenna above the surface 410 that the antennais mounted on, and the size of pedestal 400 provides the antenna with aground plane that is of a desired small-size in virtually all antennamounting conditions.

FIG. 5 shows a disk-shaped, two-antenna assembly 20 that is constructedand arranged in accordance with the invention wherein antenna assembly20 having a height 23. Antenna assembly 20 includes a first CP ringantenna 21 and a second linear monopole antenna 22 that is locatedconcentrically within ring antenna 21 and that has a height 23.

Antenna assembly 20 occupies a thin disk-shaped or cylindrical volumehaving a central axis that is shown at 31, a height that is shown at 23and an OD that is shown at 37. This overall cylindrical volume 23/37 canbe divided into three sub-volumes.

More specifically, the overall cylindrical volume 23/37 that is occupiedby antenna assembly 20 includes (1) a ring-shaped sub-volume that isoccupied by ring antenna 21 whose height is shown at 23, whose OD isshown at 37, and whose ID is shown at 38, (2) a cylindrical sub-volumethat is occupied by monopole antenna 22 whose height is shown at 23 andwhose OD is shown at 39, and (3) a ring-shaped void or openingsub-volume 30 having a height shown at 23, having an OD shown at 38, andhaving an ID shown at 39. Non0limitang example dimensions are about 9 mmfor height 23, about 70 mm for OD 37, about 46 mm for ID 38, and about18 mm for diameter 39.

Ring antenna 21 can be characterized as a relatively narrow-tracemeanderline metal ring antenna. Monopole antenna 22 can be characterizedas a terrestrial top-loaded metal disk monopole antenna that is shuntmatched. Monopole antenna 22 includes two metal posts 68, and monopoleantenna 22 is top-loaded by a metal disk 24 in order to providecapacitive loading, thus aiding in reducing the height 23 of antennaassembly 20.

While monopole antenna 22 is shown as having two metal posts 68 thatsupport metal disk 24 and are spaced at generally equal distances onopposite sides of the central axis 31 of antenna assembly 20, it iswithin the spirit and scope of this invention to provide other metalmonopole post configurations to support metal disk 24. For example, thetwo metal posts 68 shown in FIG. 5 can be replaced by one metal postthat extends generally coincident with axis 31 and that supports metaldisk 24 on the top end thereof.

In the FIG. 5 embodiment of the invention, ring antenna 21 was formed inthe shape of a narrow-trace, meandering or zig-zag, metal resonant ring25 having four generally identical 90 degree sections, one 90 degreesection of which is identified by dimension 40.

The behavior of ring 25's electrical resonance can be described as atransverse magnetic mode with a standing wave of two wavelengths aroundresonant ring 25 (i.e., the TM₂₁ mode).

Ring antenna 21 and monopole antenna 22 both radiate in a conicalradiation pattern (not shown), with the axis 31 of the conical patternextending generally perpendicular to the planar top surface 29 ofantenna assembly 20 that contains both metal resonant ring 25 and metaldisk 24.

A minimal amount of dielectric material surrounds monopole antenna 22 inorder to provide antenna 22 with a large bandwidth. That is, thegenerally cylindrical and open ring-shaped space 30 that is internal ofring antenna 21 and that surrounds monopole antenna 12 is air in thisembodiment of the invention.

The top-loading metal disk 24 of monopole antenna 22 is generallycoplanar with the resonant metal ring 25 of ring antenna 21. As statedabove, in this embodiment of the invention resonant ring 25 is tuned forthe TM₂₁ mode of operation, and resonant ring 25 is fed by a metal feedpost 26 and its series-connected capacitor 27.

Ring antenna 21 is dielectrically loaded to reduce its physical size bypositioning a low-dielectric plastic or dielectric ring 28 underresonant ring 25. As with ring antenna 21, plastic ring 28 has a heightshown at 23, an OD shown at 37, and an ID shown at 38. The top planarsurface of plastic ring 28 serves as a mechanical support for aring-shaped and top-located dielectric substrate 29 that carries metalring 21. Plastic ring 28 is shown as having four 90 degree segments,however plastic ring 28 can be formed as a single structural member.

Mechanical support for feed post 26, metal monopole posts 68, and for ametal ground plane 35 is provided by a PCB 34 having a bottom surface 35that cooperates with a metal ground plane for use by both CP ringantenna 21 and monopole antenna 22.

The OD 41 of metal resonant ring 25 is reduced by providing ring 25 inthe form of a meanderline, as shown. This metal meanderline, whichprovides for the TM₂₁ mode of operation of ring antenna 21, has a sinewave type of octagonal symmetry due to the nature of the TM₂₁ mode ofoperation. Each of the TM₂₁ modes of operation contributes a standingwave of four dipoles that extend around the 360-degree circumference ofmetal resonant ring 25. When both orthogonal TM₂₁ modes are excited, tothereby generate CP, eight standing wave dipole currents flow on metalresonant ring 25.

The metal feed post 26 for ring antenna 21 is physically positioned atthe middle between the peaks of two orthogonal modes. Hence, feed 26excites both TM₂₁ modes with equal amplitude. Any degeneracy that mayexist between the two TM₂₁ modes is broken by providing four 90-degreespaced metal perturbations or “mode separators” 36 within the metalmeanderline that makes up resonant ring 25.

In FIG. 5 each metal perturbation 36 places a capacitance at the peak,or antinode, of the electric field of that perturbation mode. That is,capacitance is placed where no current flows, and consequently theresonant frequency decreases.

Perturbations 36 also affect the orthogonal mode, thus causing a reducedinductance because peak currents flow at the position of eachperturbation 36 for its orthogonal mode. Hence, the resonance frequencyof that perturbation's orthogonal mode increase. The two orthogonalmodes then resonate at different frequencies, this being a necessarycondition for self-resonant CP.

One metal mode separator 36 is located at each of the four electricfield peaks of one of the orthogonal modes. This construction andarrangement preserves the symmetry of CP ring antenna 21 and providessymmetrical radiation patterns for CP ring antenna 21.

The metal resonant ring 25 of ring antenna 21 and the metal top-loadingdisk 24 of monopole antenna 22 are generally coplanar (i.e., both havegenerally the same height 23) in order to provide optimal bandwidth forboth antenna. Thus, each of the two antenna 21 and 22 have the largestpossible physical size within a given height 23 of the low profileantenna assembly 20.

One advantage of FIG. 5's coplanar geometry is that antenna assembly 20and its RF electronics (not shown) can share the same annular space oropening 30. That is, the antenna's electronic components can be placedon the top surface of PCB 34 and within the annular space 30, thuspreserving a low profile 23 for antenna assembly 20 and its RFelectronic components.

Other antenna, such as patch antenna, require that the antenna's RFelectronics be placed under the antenna's ground plane, and hence theoverall height of the antenna is increased. Thus, other antenna provideless potential for a low physical profile, and have less bandwidth thandoes the present invention.

The above-described FIG. 4 wide-trace embodiment of the invention hascertain advantages when compared to the above-described FIG. 5narrow-trace embodiment of the invention.

The gain from the wide-trace ring 103 of FIG. 4 peaks at a lowerelevation angle than the gain from the narrow-trace ring of FIG. 5. Morespecifically, the wide-trace ring 103 of FIG. 4 provides more gaincloser to the horizon because only the E fields around the OD ofwide-trace ring 103 contribute to radiation from wide-trace ring 103. Inaddition, wide-trace ring 103 is relatively easy to feed because a lowimpedance feed point, typically about from 50 to 100 ohms, can be foundby moving FIG. 4's feed post 135 radially inward toward the ID ofwide-trace ring 103.

The narrow-trace ring 21 of FIG. 5 has less gain closer to the horizonbecause the E fields around its OD and the opposite E fields around itsID both contribute to radiation. Radiation from the opposite E fieldstend to cancel radiation from the E fields around the OD (for example,see MICROSTRIP ANTENNA DESIGN HANDBOOK, R. Garg, P. Bhartia, I. Bahl,and A. Ittipiboon, Chapter 5, Artech House). This radiation-cancellationis more dominant along the horizon. Hence gain from narrow-trace ring 21of FIG. 5 peaks at a higher elevation angle than does the gain from awide-trace ring. In addition, a narrow-trace ring such as 21 of FIG. 5may be more difficult to feed due to its high impedance.

FIGS. 6A and 6B, respectively, show the S-parameters versus frequencyand the Smith chart of FIG. 5's two-antenna assembly 20.

The CP frequency is indicated by a notch or tight loop in the FIG. 6BSmith chart. At TM₂₁ resonance, coupling between ring antenna 21 andmonopole antenna 22 decreases due to cancellation of the fields in thecenter 31 of ring antenna 21 at the resonance frequency.

FIGS. 7A and 7B show an embodiment of the invention wherein atwo-antenna assembly 50 includes two metal feeds 51 and 52 for ringantenna 21 in order to generate CP excitation. The two feeds 51 and 52are physically placed so as to excite one of the antenna's orthogonal,degenerate, TM₂₁ modes. As stated above, each mode has a peak in theelectric field with a periodicity of every 90 degrees around ringantenna 21. Hence, there is a null in the excited mode at 45+/−n*90-degrees from each of the two feed points 51/52. The secondorthogonal mode is excited in one of these nulls in the first orthogonalmode, and the phase is +/−90-degrees in order to generate CP. In FIGS.7A and 7B the two metal feeds 51/52 are physically separated by about135 degrees of ring antenna 21. The input impedance of ring antenna 21at resonance is over 500 ohms, thus the FIG. 7A configuration requiresthat a matching circuit (not shown) be connected in circuit with each ofthe two feed posts 51/52.

FIG. 7B provides a capacitance 53 that is connected between each of thetwo metal feed posts 51/52 and ring antenna 21. This configurationreduces the input impedance at the base 54 of each of the two feed posts51/52, thus a less reactive matching circuit is required in the FIG. 7Bconfiguration.

FIGS. 8A and 8B show other techniques for applying metal perturbationsto CP ring antenna 21 in order to generate self-resonance in the absenceof an externally-located quadrature feed network. The single mode metalperturbation 60 shown in FIG. 8A is placed at one peak in the electricfield, and as a result, degeneracy between the modes is broken. When anumber of metal mode perturbations are used, for example, but notlimited to, four mode perturbations 61 as is shown in FIG. 8B, each ofthe four metal perturbations 62 can be smaller in physical size than thesingle metal perturbation 60 of FIG. 8A. As a result, the radiationpattern of ring antenna 21 of FIG. 8B is more symmetric.

FIG. 9 shows an embodiment of the invention wherein a two-antennaassembly 65 in accordance with the invention includes theabove-described monopole antenna 22 and a ring antenna 21 that includesa narrow metal ring 61 in the form of a circle for producing the TM₂₁mode of operation. That is, metal ring of 61 is not a meandering metalline as is shown at 21 in FIG. 5.

Circular metal ring 61 of FIG. 9 requires more dielectric loading, andthis dielectric loading is provided by a dielectric ring 66. Thisconstruction and arrangement achieves the same small OD 37 for antennaassembly 65 that is achieved by antenna assembly 20 of FIG. 5.

Ring antenna 21 of FIG. 9 includes four metal perturbations 67 that arephysically located at 90 degrees, and that operate in the manner of thefour above-described metal perturbations 36 of FIG. 5. In addition,monopole antenna 22 of FIG. 9 includes two metal posts 68 as shown inFIG. 5, and ring antenna 21 includes one metal feed post 26 and acapacitive element 168.

FIG. 10 shows another multi-layer embodiment of a dual channel satelliteantenna in accordance with the invention wherein a two-antenna assembly300 includes a generally centrally-located monopole antenna 301 and aTM₂₁ solid-patch wide-ring antenna 302, wherein the top disk 302 ofmonopole antenna 301 can be placed coplanar with the ring-shapedradiating element 305 of ring antenna 302, or wherein the top metal disk302 of monopole antenna 301 can be located above the plane ofring-shaped radiating element 305 as is shown in FIG. 10, and wherein anumber of generally evenly spaced cutouts 306 are provided in theassembly's disk-shaped dielectric member 307 to selectively provideinductive loading of ring antenna 302.

That is, instead of providing a coplanar TM₂₁ ring-shaped radiatingelement and a monopole radiating element, as above-described, the FIG.10 embodiment provides a monopole radiating element that either extendshigher than the ring-shaped patch 305, or the top of the monopoleradiating element may be coplanar with the ring-shaped patch 305.

In this FIG. 10 embodiment of the invention a PCB 141 is provided tosupport both a wide ring-shaped patch 305 and two metal monopole post141 and 142, and feed to wide ring-shaped patch 305 is provided by wayof metal feed post 143. An advantage of using this FIG. 10 embodiment ofthe invention is that the input impedance of ring-shaped patch 305 iseasy to tune merely by placing its feed point 143 close to the middle ofpatch 305, where the impedance of patch 305 is lower.

Wide ring-shaped radiating element 305 approximates a patch radiatingelement due to its relatively large width. For example in an embodimentof the FIG. 10 invention wherein the OD of antenna assembly 300 wasabout 85 mm, the width of ring-shaped radiating element 305 was about 80mm, and the above-mentioned brand NORYL (DK of about 2.6) was used toform dielectric ring 307, to thereby provide dielectric loading.

The above-described antennas and antenna assemblies can be manufacturedin various manners including, but not limited to, insert molding,two-shot molding, and by the use of an etched PCB and stamped metalparts.

One application for an antenna in accordance with the invention is tomount the antenna on the fiberglass top of a vehicle such as a truck.When this antenna has about a 112 mm diameter ground plane, the antennawill work better at low elevations than an antenna that is mounted onthe large metal top of a conventional automobile, due to the groundplane effects above-discussed.

Another application for antenna in accordance with the invention is tomount the antenna on an automobile's front-located plastic dashboard,which mounting-location usually does not provide a ground plane effect.It is worth noting that such a dashboard-mounted antenna generally doesnot provide an omni-directional radiation pattern, and as a result,radiation out of the back of the automobile suffers. Thus, one antennacan be placed on the dashboard, a second antenna can be placed at theback of the automobile, and a diversity algorithm can be used. Thisabove two-antenna configuration tends to guarantee good satellitereception for an automobile having internal antenna.

Considering 20-degree elevation gain in the northern states of the U.S.,when a large-area ground plane is used the gain of the above-describedTM₂₁ antennas has a steep roll-off at 20 degrees above the horizon,which effect can impact reception in the northern states of the US.However, this low elevation gain is improved by placing the TM₂₁ antennaon a metal pedestal.

FIG. 11 shows an embodiment of the invention wherein antenna 100 of FIG.4 is placed on the top of a disk-shaped or cylindrical-shaped metalpedestal 400 that provides an optimum-size ground plane for antenna 100.Generally speaking, FIG. 11 provides a metal pedestal/can 400 that isplaced under antenna 100 which assembly is then mounted on a very largearea metal ground plane, for example a metal automobile roof 410.Usually the FIG. 11 assembly of antenna 100 and pedestal/can 400 wouldbe used when there is a large-area ground plane 410 directly underassembly 100/400.

Without limitation thereto, in the FIG. 11 embodiment of the inventionmetal pedestal 400 had a height 401 of about 20 mm and a diameter 402 ofabout 112 mm. In this embodiment of the invention, both large satellitegain and large terrestrial gain are achieved at lower elevation angles,this being of a particularly advantage in northern states such as Maineand Washington.

Metal pedestal 400 operates to increase the height of antenna 100 byabout 20 mm. However the reception of antenna 100 is about 3 dB better,and from a performance standpoint the pattern of TM₂₁ antenna 100 onmetal pedestal 400 is about 1 Db better than that of a tall quadrifillerantenna at 20 degrees.

The terrestrial pattern of antenna 100 on metal pedestal 400 is alsovery good, with the antenna's terrestrial gain being increased by about2 dB at the horizon.

Because antenna 100 is ground-plane-dependent, the antenna's radiationpattern can be modified by using small-diameter/area metal ground planesand/or metal pedestals such as pedestal 400. Hence, antennas can becustomized for inside-the-car or outside-the-car applications.Quadrifillar antenna can not provide this feature because they are notground plane dependent.

A crossed dipole antenna is ground plane dependent, and placing such anantenna on a metal pedestal would likely exaggerate the cardioid dip atthe zenith of its radiation pattern. However, such a pedestal-mountedcross dipole antenna would be taller than the embodiment of FIG. 11.Also, the use of a small ground plane will make the crossed dipolepattern of such an antenna more directional toward the zenith.

Thus, the constructions and arrangements of embodiments of the presentinvention provide a distinct advantage wherein the antenna's groundplane can be treated as a design variable.

What is claimed is:
 1. A disk-shaped two-antenna assembly, comprising: adielectric ring having an outer diameter, an inner diameter, aring-shaped and generally planar top surface, and a ring-shaped andgenerally planar bottom surface that is generally parallel to saidring-shaped top surface; a disk-shaped metal ground plane associatedwith said ring-shaped bottom surface of said dielectric ring; aring-shaped metal radiating element abutting said ring-shaped topsurface of said dielectric ring; a linear metal radiating element; saidlinear radiating element having a bottom end associated with andinsulated from said disk-shaped ground plane at a location that isgenerally concentric with said disk-shaped ground plane; said linearradiating element having a top end occupying a plane that is eithercommon with a plane that is occupied by said ring-shaped metal radiatingelement or is above said plane occupied by said ring-shaped metalradiating element; first antenna feed means connected to said ringshaped metal radiating element; and second antenna feed means connectedto said generally linear metal radiating.
 2. The two-antenna assembly ofclaim 1 including: a disk-shaped printed circuit board associated withsaid ring-shaped bottom surface of said ring-shaped dielectric ring;said metal ground plane being located on a bottom surface of saidprinted circuit board.
 3. The two-antenna assembly of claim 1 including:a metal disk concentrically mounted on said top end of said linear metalradiating element; said metal disk having a diameter that is less thansaid inner diameter of said dielectric ring; and said metal diskoccupying a plane that is generally parallel to said ground plane. 4.The two-antenna assembly of claim 1 including: at least one metalperturbation connected to said ring-shaped metal radiating element. 5.The two-antenna assembly of claim 1 including: four metal perturbationsconnected to said ring-shaped metal radiating element; said four metalperturbations being located at 90 degree intervals about a circumferenceof said ring-shaped metal radiating element.
 6. The two-antenna assemblyof claim 1 wherein said ring-shaped metal radiating element is arelatively narrow ring-antenna radiating element metal line thatmeanders back and forth across said ring-shaped top surface of saiddielectric ring.
 7. The two-antenna assembly of claim 1 wherein saidring-shaped metal radiating element is a relatively narrow ring-antennaradiating element that forms a circle on said ring-shaped top surface ofsaid dielectric ring.
 8. The two-antenna assembly of claim 1 whereinsaid ring-shaped metal radiating element is a relatively widering-antenna radiating element that forms a circle on said ring-shapedtop surface of said dielectric ring.
 9. The two-antenna assembly ofclaim 1 wherein said ring-shaped metal radiating element is a widepatch-antenna radiating element that forms a circle on said ring-shapedtop surface of said dielectric ring.
 10. The two-antenna assembly ofclaim 1 including: a plurality of voids formed in said dielectric ring.11. The two-antenna assembly of claim 1 including: an electricallyreactive element connecting said first metal antenna feed means to saidring shaped metal radiating element.
 12. The two-antenna assembly ofclaim 1 wherein said ring antenna is a CP antenna, and wherein saidring-shaped metal radiating element comprises a ring-shaped metal linethat meanders back and forth across said ring-shaped top surface of saiddielectric ring to form four generally identical 90 degree long sectionsthat support an electromagnetic wave having a length of two wavelengthsthat extend about the 360 degree circumference of said ring-shaped metalline.
 13. The two-antenna assembly of claim 12 including: four metalperturbations associated with said ring-shaped metal line; said fourmetal perturbations being located at 90 degree intervals about saidring-shaped metal line.
 14. The two-antenna assembly of claim 13including: a metal disk concentrically mounted on said top end of saidlinear metal radiating element so as to occupy a plane that is generallycommon with said ring-shaped metal radiating element; said metal diskhaving a diameter that is less than said inner diameter of saiddielectric ring.
 15. The two-antenna assembly of claim 14 including: atleast one electrically reactive element connecting said first metalantenna feed means to said ring shaped metal radiating element.
 16. Thetwo-antenna assembly of claim 15 wherein said metal ground plane iscarried by a bottom surface of a printed circuit board.
 17. Thetwo-antenna assembly of claim 16 wherein said two feed connections arephysically spaced by about 135 degrees.
 18. The two-antenna assembly ofclaim 12 wherein said first metal antenna feed means comprises two feedconnections to said ring shaped metal line, said two feed connectionsbeing physically spaced about said ring shaped metal line in a manner togenerate CP excitation of said ring shaped metal line.
 19. Thetwo-antenna assembly of claim 1 wherein a diameter of said disk-shapedground plane is about 20 percent greater than a diameter of saiddielectric ring.
 20. The two-antenna assembly of claim 1 wherein saiddisk-shaped metal ground plane is formed by a top surface of a metalpedestal.
 21. The two-antenna assembly of claim 20 wherein a diameter ofsaid top surface of said metal pedestal is about 20 percent greater thana diameter of said dielectric ring.
 22. A method of making a low profiletwo-antenna assembly that contains a ring antenna and a linear monopoleantenna, said two-antenna assembly being in the shape of a disk having acentral axis, a diameter and a thickness, the method comprising thesteps of: providing a ring-shaped dielectric member having an innerdiameter, an outer diameter that is generally equal to said diameter ofsaid two-antenna assembly, a ring-shaped top planar surface that extendsgenerally perpendicular to said central axis of said two-antennaassembly, a ring-shaped bottom planar surface that extends generallyparallel to said ring-shaped top planar surface, and a thickness that isgenerally equal to said thickness of said two-antenna assembly;providing a circular metal radiating element on said top surface of saidring-shaped dielectric member; providing a linear metal radiatingelement having a top end, a bottom end, and a length that is at leastequal to said thickness of said two-antenna assembly; and mounting saidlinear metal radiating element generally coincident with said centralaxis of said two-antenna assembly, with said bottom end generallycoincident with said bottom surface of said ring-shaped dielectricmember.
 23. The method of claim 22 wherein said thickness of saidtwo-antenna assembly is smaller than said diameter of said two-antennaassembly.
 24. The method of claim 22 including the step of: providing adisk-shaped metal ground plane having a diameter that is at least equalto said diameter of said ring-shaped dielectric member associated withsaid bottom surface of said ring-shaped dielectric member.
 25. Themethod of claim 24 including the steps of: providing a thin anddisk-shaped dielectric member intermediate said ground plane and saidbottom surface of said ring-shaped dielectric member; and mounting saidbottom end of said linear metal radiating element on said dielectricmember.
 26. The method of claim 22 including the step of: providingpedestal having a top metal surface associated with said bottom surfaceof said ring-shaped dielectric member.
 27. The method of claim 22including the steps of: providing a thin metal disk having a center anda diameter that is no greater than said inner diameter of saidring-shaped dielectric member; and mounting said metal disk on said topend of said linear metal radiating element such that said center of saidmetal disk is generally coincident with said center axis of saidtwo-antenna assembly.
 28. The method of claim 22 including the step of:providing said circular metal radiating element as a narrow ring-antennaradiating element that meanders back and forth across said top surfaceof said ring-shaped dielectric member.
 29. The method of claim 22including the step of: providing said circular metal radiating elementas a narrow ring-antenna radiating element that forms a circle on saidtop surface of said ring-shaped dielectric member.
 30. The method ofclaim 22 including the step of: providing said circular metal radiatingelement as a wide ring-antenna radiating element that forms a circle onsaid top surface of said ring-shaped dielectric member.
 31. The methodof claim 22 including the step of: providing said circular metalradiating element as a wide patch-antenna radiating element that forms acircle on said top surface of said ring-shaped dielectric member. 32.The method of claim 31 including the step of: forming inductive-loadingvoids in said ring-shaped dielectric member.
 33. The method of claim 31including the steps of: providing a thin metal disk having a center anda diameter that is no greater than an inner diameter of said circle; andmounting said metal disk on said top end of said linear metal radiatingelement such that said center of said metal disk is generally coincidentwith said center axis of said two-antenna assembly.
 34. The method ofclaim 33 including the step of: providing a thin disk-shaped dielectricmember intermediate said disk-shaped metal ground plane and said bottomsurface of said ring-shaped dielectric member.
 35. The method of claim34 wherein said thickness of said two-antenna assembly is smaller thansaid diameter of said two-antenna assembly.
 36. The method of claim 22wherein said circular metal radiating element is a CP ring-antennaradiating element, including the step of: providing said CR ring-antennaradiating element as a metal pattern that meanders back and forth acrosssaid top surface of said ring-shaped dielectric member to form fourgenerally identical 90 degree long metal pattern sections for support ofan electromagnetic wave having a length of two wavelengths extendingaround said metal pattern.
 37. The method of claim 36 including the stepof: providing four metal perturbations connected to said metal pattern;and locating said four metal perturbations at 90 degree intervals aboutsaid metal pattern.
 38. The method of claim 37 including the step of:providing a metal disk concentrically mounted on said top end of saidlinear metal radiating element; said metal disk having a diameter thatis less than said inner diameter of said ring-shaped dielectric member.39. The method of claim 38 including the step of: providing at least oneelectrically reactive element connecting metal antenna feed means tosaid circular metal radiating element.
 40. The method of claim 39wherein said disk-shaped dielectric member is a printed circuit board.41. The method of claim 36 including the step of: providing two feedconnections to said circular metal radiating element that are physicallyspaced about said circular metal radiating element in a manner togenerate CP excitation of said circular metal radiating element.
 42. Themethod of claim 41 wherein said two feed connections are physicallyspaced by about 135 degrees.
 43. A two-antenna assembly containing botha CP ring antenna and a linear monopole antenna, said two-antennaassembly being in the shape of a disk having a central axis, a diameterand a thickness that is less than said diameter, the two-antennaassembly comprising; a ring-shaped dielectric member having an innerdiameter, an outer diameter that is generally equal to said diameter ofsaid two-antenna assembly, a ring-shaped top planar surface that extendsgenerally perpendicular to said central axis, a ring-shaped bottomplanar surface that extends generally parallel to said ring-shaped topplanar surface, and a thickness that is generally equal to saidthickness of said two-antenna assembly; a disk-shaped metal ground planeassociated with said bottom surface of said dielectric member, saidground plane having a diameter that is generally equal to said diameterof said ring-shaped dielectric member; a circular metal radiatingelement on said top surface of said ring-shaped dielectric member; saidcircular metal radiating element for supporting an electromagnetic wavehaving a length of two wavelengths extending 360 degrees around said topsurface of said ring-shaped dielectric member; a linear metal radiatingelement having a top end, a bottom end, and a length that is at leastequal to said thickness of said two-antenna assembly; said linear metalradiating element being positioned coincident with said central axis,with said bottom end associated with, but insulated from, said groundplane; and a planar metal disk concentrically mounted on said top end ofsaid linear metal radiating element such that a plane of said diskextends generally perpendicular to said central axis; a diameter of saiddisk being less than said inner diameter of said ring-shaped dielectricmember.
 44. The two-antenna assembly of claim 43 including: four equallyspaced metal perturbations electrically connected to said circular metalradiating element.
 45. The two-antenna assembly of claim 44 including:at least one electrically reactive element connecting an antenna feedmeans to said circular metal radiating element.
 46. The two-antennaassembly of claim 44 including: two metal feeds connected to saidcircular metal radiating element; said two feeds being physically spacedabout said ring antenna radiating element in a manner to generate CPexcitation of said circular metal radiating element.
 47. The two-antennaassembly of claim 46 wherein said two feeds are physically spaced byabout 135 degrees.
 48. The two-antenna assembly of claim 43 wherein saidmetal ground plane is a thin and planar metal member.
 49. Thetwo-antenna assembly of claim 48 wherein a diameter of said thin andplanar metal member is about 20 percent greater than a diameter of saidring-shaped dielectric member.
 50. The two-antenna assembly of claim 43wherein said metal ground plane is a cylindrical-shaped pedestal havinga planar top metal surface that forms said metal ground plane.
 51. Thetwo-antenna assembly of claim 50 wherein a diameter of said top metalsurface is about 20 percent greater than a diameter of said ring-shapeddielectric member.
 52. A disk-shaped two-antenna assembly, comprising: aring-shaped dielectric member having a central axis, having an outerdiameter, having an inner diameter, having a thickness, having acircular top surface that lies in a plane extending generallyperpendicular to said central axis, and having a circular bottom surfacethat lies in a plane extending generally perpendicular to said centralaxis; a circular metal ground plane having a peripheral portion thereofassociated with said circular bottom surface of said dielectric member;said ground plane having a diameter that is at least as great as saidouter diameter of said dielectric member; said ground plane and saidinner diameter of said dielectric member defining a cylindrical void forthe placement of electronic components associated with said two-antennaassembly; a ring-shaped metal antenna radiating element on said topcircular surface of said dielectric member; and a linear metal antennaradiating element located generally coincident with said central axis,having a top end, having a bottom end associated with and electricallyinsulated from said ground plane, and having a length at least equal tosaid thickness of said dielectric member.
 53. The two-antenna assemblyof claims 52 including: at least two metal shield plates electricallyconnected to said ground plane and located within an upper portion ofsaid cylindrical void intermediate said ground plane and said top end ofsaid linear antenna radiating element; said at least two shield platesbeing physically spaced from said linear antenna radiating element. 54.The two-antenna assembly of claim 53 including: a metal disk having acenter thereof mounted on said top of said linear antenna element, andhaving a diameter that is no greater than said inner diameter of saiddielectric member.
 55. The two-antenna assembly of claim 54 wherein saiddisk occupies a plane generally coincident with said top circularsurface of said dielectric member.
 56. The two-antenna assembly of claim54 wherein said disk occupies a plane that is located above said topcircular surface of said dielectric member.
 57. The two-antenna assemblyof claim 52 wherein said ring-shaped metal antenna radiating elementincludes cutout portions that operate to provide reactive loading. 58.The two-antenna assembly of claim 52 wherein said ring-shaped metalantenna radiating element includes cutout portions that operate as modeseparators.
 59. The two-antenna assembly of claim 52 wherein saidcircular metal ground plane is a top metal surface of acylindrical-shaped pedestal.